1. Field of the Invention
This invention relates to a machine tool comprising a column which is slidable in a predetermined direction.
2. Description of Related Art
A machine tool including a column slidable in a z-axis direction (i.e., frontward and rearward) on a bed and a headstock translatable in a y-axis direction (i.e., upward and downward) along the column is known in the art (e.g., JP 7-88737 A). Such a machine tool 51 is now described briefly with reference to FIG. 2. In FIG. 2, X axis, Y axis and Z axis are axes perpendicular to one another, and are oriented such that the X axis extends leftward and rightward, the Y axis extends upward and downward, and the Z axis extends frontward and backward; thus, the terms “x-axis direction”, “y-axis direction” and “z-axis direction” are used to designate a leftward-rightward direction, an upward-downward direction and a frontward-backward direction, respectively.
The machine tool 51 includes a bed 52, a pair of rail members 53 extending in the z-axis direction on top of the bed 52, a column 54 attached, movably in the z-axis direction, to the rail members 53, and a headstock 56 including a spindle 57. The headstock 56 is provided at a front side of the column 54 and configured to be translatable in the y-axis direction (i.e., slidable along the front side of the column 54).
When this machine tool 51 is operated for machining, the headstock 56 is moved in the y-axis direction. However, the headstock 56 moved upward brings the center of gravity of the column 54 upward accordingly; therefore, the structural strength and stability of the column 54 would disadvantageously be lowered. This problem may possibly be overcome by providing the column 54 with increased rigidity, but this would create several other problems such as an undesirable increase in the mass of the column 54, upsizing of the machine tool 51 in its entirety, and upsizing of a motor or the like for driving the column 54.
It would thus be desirable to provide a machine tool in which a support member with a headstock mounted thereto is kept strong and stable enough to withstand the upward and downward movement of the headstock without upsizing of the support member or the like. The present invention has been made in view of the aforementioned problems, and illustrative, non-limiting embodiments of the present invention may overcome the above disadvantages and other disadvantages not described above.